It preserves a variety of fossil remains, including those of dinosaurs, and contains direct evidence of the mass mortality that occurred at the Cretaceous-Paleogene boundary.
Some of these remains show signs of severe abrasion and erosion, however, implying that they may be re-worked from older deposits.
[8] In addition, recent studies have found evidence of high iridium concentration and shocked quartz within the MFL, suggesting that the MFL represents a thanatocoenosis formed from an ecosystem collapse during the Cretaceous-Paleogene extinction event.
[3] Based on Case (1996) and Boles et al (2024):[3][9] A number of fossil birds are known from the greensands of the formation.
The Hornerstown serves as the type locality for all these genera and species: Anatalavis A. rex Graculavus G. velox Laornis L. edwardsianus Palaeotringa P. littoralis P. vagans Telmatornis T. priscus Tytthostonyx T. glauconiticus The tyrannosauroid Dryptosaurus is sometimes referred to this formation, as its remains were found in the New Egypt Formation, which is sometimes considered a part of the Hornerstown.